Encapsulation of electroluminescent devices with shaped spacers

ABSTRACT

A method of encapsulating a device is disclosed. Spacer particles are randomly located in a device region to prevent a cap mounted on the substrate from contacting the active components when pressure is applied to the cap, thereby protecting the active components from damage. The spacer particles comprise a base and an upper portion, the base being at least equal to or wider than the upper portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims the benefit of priority under 35 U.S.C. Section 120 of U.S. application Ser. No. 10/065,254, filed Sep. 30, 2002, which is a continuation-in-part of U.S. application Ser. No. 09/989,362, filed Nov. 20, 2001, which is a continuation-in-part of International Application Serial No. PCT/SG99/00143, filed Dec. 17, 1999. The disclosure of each prior application is considered part of and is incorporated by reference in the disclosure of this application.

BACKGROUND

FIG. 1 shows an OLED device 100. The OLED device comprises a substrate 101, and one or more organic functional layers 102 formed between first and second electrodes 104 and 106. The electrodes can be patterned to form, for example, a plurality of OLED cells to create a pixelated OLED device. OLED cells are located in the device region where the cathodes and anodes overlap. Bond pads 110, which are coupled to the first and second electrodes, are provided to enable electrical connections to the OLED cells.

To protect the OLED cells from components of the environment such as moisture and/or air, a cap 112 encapsulates the device. The active materials of the OLED cells are sensitive and can be easily damaged due to mechanical contact with, for example, the cap. To prevent damage to the OLED cells, a cap or package is used. The package provides a cavity 114 between the cap and OLED cells. The cavity allows for the placement of desiccant materials to cope with finite leakage rate of the device.

The demand for thin and flexible devices requires the use of thinner components, such as the cap and the substrate. Decreasing the thickness of the cap reduces its mechanical stability, making it more prone to bending, which can cause the cavity to collapse, thereby damaging the OLED cells. Spacer particles 116 are provided in the device region to prevent the cap from contacting the active components, thereby protecting them from damage.

However, the spherical shape of spacer particles exposes the edges of the electrode layer 106 in regions such as region 118, to react with atmospheric components such as moisture and gases (e.g., oxygen). The penetration of atmospheric components into the interior of the OLED may result in the formation of impurities at the electrode-organic material interface. These impurities may cause separation of the electrode from the organic layer. Dark, non-emitting spots may appear at the areas of separation around the spacer particles due to the lack of current flow.

As evidenced from the foregoing discussion, it is therefore desirable to provide an OLED device having improved packaging, particularly those formed on thin or flexible substrates.

SUMMARY OF THE INVENTION

The invention relates to encapsulation for devices, such as OLED devices. A cap is mounted on the substrate to encapsulate the device, forming a cavity over a device region to protect the active components from contact with the cap.

In accordance with the invention, spacer particles are provided in the device region to support the cap. The spacer particles are shaped to prevent the generation of dark spots around the spacer particles. The spacer particles comprise a base and an upper portion, the base being at least equal to or wider than the upper portion. In one embodiment, the spacer particles comprise a half-spherical shape. Spacer particles comprising other shapes such as pyramidal, cubical, prism, or other regular or irregular shapes, in which the base is at least equal to or wider than the upper portion, are also useful.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an OLED device;

FIG. 2 shows one embodiment of the invention;

FIGS. 3 a-c show spacer particles according to different embodiments of the invention; and

FIGS. 4-8 show a process for forming an OLED device in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

In one embodiment, the substrate is about 20-300 μm thick. In some cases, the thin substrate may be mechanically unstable, creating processing problems. A temporary support layer (not shown) can be employed to stabilize the substrate during the fabrication process. The temporary support layer, for example, can be provided on the backside of the substrate. In one embodiment, the temporary support layer comprises a polymer foil coated with an adhesive for attaching to the substrate. After processing, the temporary layer is removed since the device package can be used to mechanically stabilize the device.

The OLED cells comprise one or more organic layers 203 sandwiched between lower and upper electrodes. In one embodiment, the lower electrodes 204 are anodes and the upper electrodes 206 are cathodes. Forming lower electrodes that are cathodes and upper electrodes that are anodes is also useful. In one embodiment, the electrodes are patterned as strips in, for example, passive-matrix display applications. Typically, the upper and lower electrodes are patterned in first and second directions that are orthogonal to each other. The intersections of the upper and lower electrodes form the OLED cells. The cells are addressed by activating the corresponding rows and columns. Alternatively, the OLED display comprises an active-matrix. The active-matrix display comprises cells that are individually addressed by thin-film-transistors (TFTs) and capacitors formed on an electronic backplane.

A cap 210 is provided to seal the device. The cap, in one embodiment, comprises glass. Other materials, such as metal, ceramic or plastics, can also be used. The cap forms a cavity 212 that prevents damage to OLED cells caused by, for example, mechanical contact with the cap.

In accordance with one embodiment of the invention, spacer particles 208 are deposited on the substrate to prevent the cap from contacting the active components. The spacer particles are shaped to prevent the growth of dark and non-emitting spots around the particles. In one embodiment, the spacer particles comprise a base and an upper portion, the base being at least equal to or larger than the upper portion. The profile of the particles prevents regions such as 214 from being exposed to potentially deleterious components (e.g., water and oxygen) that are present in the device. In one embodiment, the spacer particles comprise a half-spherical shape, as shown in FIG. 2. To avoid causing shorts between the electrodes, the spacer particles preferably comprise a non-conductive material. In one embodiment, the spacer particles are made of glass. Spacer particles made of other types of non-conductive materials, such as silica, polymers, ceramic or photoresist, are also useful.

The average diameter of the spacer particles is preferably sufficient to maintain the desired height of the cavity, which is, for example, about 2-50 μm. The distribution of the spacer particles is preferably sufficient to ensure proper separation between the cap and OLED cells when mechanical pressure is applied to the device, without affecting the emission uniformity of the cells. The distribution may be varied to accommodate design requirements, such as the thickness of the cap, thickness of the substrate, and amount of device flexibility needed. Preferably, the distribution of the spacer particles should be selected such that their influence on the emission uniformity is invisible to the unaided human eye. In one embodiment, the density of the spacer particle distribution is about 10-1000 No/mm². Typically, the average distance between spacer particles is about 100-500 μm.

Referring to FIGS. 3 a-c, spacer particles having other geometric shapes, such as pyramidal, cubical, prism, or other regular or irregular shapes, in which the base is at least equal to or wider than the upper portion, are also useful.

FIGS. 4-8 show a process of forming an OLED device, according to one embodiment of the invention. A first conductive layer 402 is deposited on the substrate 401. The substrate can be provided with a barrier layer, such as silicon dioxide (SiO₂), beneath the conductive layer on the substrate surface prior to depositing the conductive layer. Barrier layers are particularly useful for substrates comprising soda lime glass. The barrier layer, for example, is about 20 nm thick. Various techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and plasma enhanced CVD (PECVD), can be employed to form the device layer. The conductive layer should be thin to reduce optical absorption and negative impact on subsequent film formation while satisfying electrical requirements. The conductive layer is typically about 0.02-1 μm thick.

Referring to FIG. 5, the conductive layer 402 is patterned as desired to selectively remove portions of the layer, exposing portions 504 of the substrate. The patterned conductive layer serves as first electrodes for the OLED cells. In one embodiment, the conductive layer is patterned to form strips that serve as, for example, anodes of a pixelated OLED device. The patterning process can also form connections for bond pads. Conventional techniques, such as photolithography and etching, can be used to pattern the conductive layer. Patterning techniques using a stamp are also useful.

In accordance to the invention, shaped spacer particles 502 are deposited on the substrate. The spacer particles, in one embodiment, comprise the desired shape before deposition. Alternatively, the spacer particles are patterned to form the desired shape after being deposited onto the substrate. For example, the particles may be heated to a high temperature to reflow into the desired shape on the substrate. In another embodiment, a photoresist is deposited on the substrate. The photoresist may be patterned to form the spacers with the desired shape.

In one embodiment, the spacer particles are deposited by spraying techniques (e.g., wet or dry spraying). Other techniques, such as spin coating, doctor blading or various printing methods (e.g., screen printing or transfer printing) are also useful.

In a preferred embodiment, a dry spray technique is employed to deposit the spacer particles. Dry spray techniques are described in, for example, Birenda Bahadur (Ed), Liquid Crystals: Applications and Uses, Vol. 1 (ISBN 981 02011 09). Dry spray techniques typically comprise electrostatically charging the spacer particles with a first polarity (positive or negative) and the substrate with a second polarity (negative or positive). The spacer particles are blown against the substrate with dry air supplied by a dry air sprayer. Dry air sprayers, such as a DISPA-μ R from Nisshin Engineering Co., can be used.

The use of a wet spray technique to deposit the spacer particles on the substrate is also useful. Wet spray techniques are described in, for example, Birenda Bahadur (Ed), Liquid Crystals: Applications and Uses, Vol. 1 (ISBN 9810201109).

In one embodiment, the spacer particles are randomly distributed on the substrate. The spacer particles occupy both active and non-active parts (i.e., emitting and non-emitting areas) of the device. In another embodiment, the spacer particles are confined to the non-active areas. Various techniques such as photolithography technology can be employed to pattern the coverage of the spacer particles. Alternatively, shadow mask or stencil mask technology can be used. A shadow mask with the required pattern is placed in close proximity or direct contact with the surface before deposition of the spacer particles. During the spray application process, only the regions which are exposed by the mask will be covered with spacer particles. Alternatively, a patterned dry resist film can be laminated on the bare surface. After the spacer particles are deposited, the dry resist film is cured and removed from the surface, leaving the exposed areas covered with spacer particles. A liquid resist material can also be used in a similar manner.

The spacer particles are preferably fixed to one side of the substrate to avoid any movement. In one embodiment, the spacer particles are coated with a thin layer of adhesive before deposition. The adhesive layer comprises, for example, epoxy resin or acrylic resin. In one embodiment, the adhesive is cured by heat treatment. In another embodiment, the adhesive is cured by exposure to ultraviolet radiation. In yet another embodiment, the adhesive comprises a hot melt material.

Referring to FIG. 6, one or more organic functional layers 602 are formed on the substrate, covering the spacer particles, the exposed substrate portions and conductive layer. The organic functional layers can be formed by conventional techniques, for example, wet processes such as spin coating or vacuum sublimation (for Alq₃ organic layers). Portions of the organic layers can be selectively removed to expose underlying layers in regions 604 for bond pad connections. Selective removal of the organic layers can be achieved using, for example, a polishing process. Other techniques, such as etching, scratching, or laser ablation, are also useful.

Referring to FIG. 7, a second conductive layer 704 is deposited on the substrate, covering the spacer particles and other layers formed thereon. In one embodiment, the second conductive layer is patterned to form electrode strips that serve as cathodes for a pixelated OLED device. Also, connections for bond pads can be formed during the patterning process. Alternatively, the conductive layer can be selectively deposited to form cathode strips and bond pad connections. Selective deposition of the conductive layer can be achieved with, for example, mask layers. The cathode strips are typically orthogonal to the anode strips. Forming cathode strips that are diagonal to the anode strips is also useful. The intersections of the top and bottom electrode strips form organic LED pixels.

Referring to FIG. 8, a cap 802 is mounted on the substrate to encapsulate the device. The cap creates a cavity 803, providing separation between it and the OLED cells. In one embodiment, a sealing frame 804 surrounding the cell region is prepared. Preparation of the sealing frame includes patterning the substrate, if necessary, to form an area for forming a sealing post 804 therein. Alternatively, the sealing frame can be formed on the cap. The height of the sealing post is sufficient to form a cavity 803 with the desired height. The use of a sealing frame is described in international patent application “Improved Encapsulation of Organic LED Device”, PCT/SG00/00133, which is herein incorporated by reference for all purposes.

The cap layer 802 comprises, for example, metal or glass. Other types of caps which protect the active components from the environment, such as ceramic or metallized foil, are also useful. In yet another embodiment of the invention, the cap can be stamped or etched, depending on the material used, to form a cavity separating the cap and the OLED devices.

Various techniques can be used to mount the cap layer. In one embodiment, an adhesive is used to mount the cap layer. Adhesives such as self-hardening adhesives, UV or thermal curable adhesives, or hot melt adhesives are useful. Other techniques which employ low temperature solder materials, ultrasonic bonding, or welding techniques using inductance or laser welding are also useful.

In one embodiment of the invention, a sealing dam surrounding the device region of the substrate is provided. The sealing dam supports the cap on the substrate and provides a sealing region located at an outer face of the sealing dam. The use of a sealing dam is described in international patent application “Sealing of Electronic Devices”, PCT/SG00/00133 (attorney docket number 99E05737SG), which is herein incorporated by reference for all purposes.

During the mounting process, the spacer particles may be pressed into the layers of the OLED cells. The spacer particles provide support for the cap over the area of the OLED cells, preventing the cap from contacting the active components of the device when pressure is applied to the cap. Bond pads 806 are formed to provide electrical access to the OLED cells.

As described, the process deposits the adhesive-coated spacer particles after formation of the first conductive layer. The spacer particles can alternatively be deposited at other points in the process flow. For example, the spacer particles can be deposited before the formation of the first conductive layer, before or after the formation of the second conductive layer. In effect, the spacer particles can be deposited at any point of the process prior to mounting of the cap.

The adhesive on the spacer particles is cured at some point in the process flow after the deposition of the spacer particles. In one embodiment, the adhesive is cured after the spacer particles are deposited on the substrate and before the formation of the organic layers. In another embodiment, the adhesive is cured after the spacer particles are applied to the first active organic layer and before the formation of the remaining layers. In another embodiment, the adhesive is cured after the spacer particles are applied to the second organic layer and before the formation of the remaining layers. In yet another embodiment, the adhesive is cured after the spacer particles are applied to the second conductive layer and before the encapsulation of the OLED device. Spacer particles can also be useful in providing support in other types of devices that employ cavity packages. Such devices include, for example, electrical devices, mechanical devices, electromechanical devices, or microelectromechanical systems (MEMS).

While the invention has been particularly shown and described with reference to various embodiments, it will be recognized by those skilled in the art that modifications and changes may be made to the present invention without departing from the spirit and scope thereof. The scope of the invention should therefore be determined not with reference to the above description but with reference to the appended claims along with their full scope of equivalents. 

1. A method for forming a device, comprising: providing a substrate with a device region; applying a layer of adhesive on spacer particles, the spacer particles comprising a base and an upper portion, the base being at least equal to or wider than the upper portion; depositing the spacer particles on the substrate; curing the layer of adhesive on the spacer particles; and mounting a cap on the substrate to encapsulate the device, the cap forming a cavity over the device region, wherein the spacer particles are capable of supporting the cap when pressure is applied to the cap.
 2. The method of claim 1 wherein the device comprises an OLED device.
 3. The method of claim 1 wherein the spacer particles comprise a nonconductive material.
 4. The method of claim 1 wherein the step of depositing the spacer particles comprises dry spraying.
 5. The method of claim 4 wherein the spacer particles occupy active and non-active parts of the device region.
 6. The method of claim 4 wherein the spacer particles occupy non-active parts of the device region.
 7. The method of claim 4 further comprising patterning a region covered by the spacer particles using photolithography.
 8. The method of claim 4 further comprising using a shadow mask to define a region covered by the spacer particles on the substrate.
 9. The method of claim 4 further comprising defining a region covered by the spacer particles on the substrate using dry resist patterning.
 10. The method of claim 1 wherein the step of depositing the spacer particles comprises wet spraying.
 11. The method of claim 10 wherein the spacer particles occupy active and non-active parts of the device region.
 12. The method of claim 10 wherein the spacer particles occupy non-active parts of the device region.
 13. The method of claim 10 further comprising patterning a region covered by the spacer particles using photolithography.
 14. The method of claim 10 further comprising using a shadow mask to define a region covered by the spacer particles on the substrate.
 15. The method of claim 1 wherein the step of depositing the spacer particles comprises spin coating, doctor blading, screen printing or transfer printing.
 16. The method of claim 1 wherein curing the layer of adhesive comprises thermally curing the layer of adhesive.
 17. The method of claim 1 wherein the curing the layer of adhesive comprises curing the layer of adhesive with ultraviolet light.
 18. The method of claim 1 wherein the adhesive comprises hot melt material.
 19. A method for forming a device, comprising: providing a substrate with a device region; forming a plurality of spacer particles on the substrate, the spacer particles comprising a base and an upper portion, the base being at least equal to or wider than the upper portion; and mounting a cap on the substrate to encapsulate the device, the cap forming a cavity over the device region, wherein the spacer particles are capable of supporting the cap when pressure is applied to the cap.
 20. The method of claim 19 wherein the step of forming a plurality of spacer particles on the substrate comprises: depositing particles on the substrate; and heating the particles to a high temperature to cause the particles to flow and form the spacer particles having the base that is at least equal to or wider than the upper portion.
 21. The method of claim 19 wherein the step of forming a plurality of spacer particles on the substrate comprises: depositing a photoresist on the substrate; and patterning the photoresist into the spacer particles having the base that is at least equal to or wider than the upper portion. 